1. Field of the Invention
Present invention is related to a sound-absorbing material, especially to a sound-absorbing material absorbing middle to low frequency of sound.
2. Description of the Prior Art
Nowadays, buildings become not only provide shelters but also symbolize quality of life. Governments and technology workers have drawn attention to noise problems. Noise may be controlled mainly in two ways, that is, to reduce or eliminate from a source of noise or to isolate the noise by using sound-absorbing material.
Since it is not easy to find where the noise came from, various kinds of sound-absorbing materials such like acoustic foams or fabrics were developed. With reference to FIG. 11, conventional sound-absorbing material mainly absorbs the sound in high frequency over 1000 Hz and performs bad absorption ability at middle to low frequency. Many researches indicate that middle to low frequency may cause more serious damages to human's healthy than high frequency. Thus, creating a sound-absorbing material mainly absorbing middle to low frequency or even a full frequency sound-absorbing material is necessary.